Numerous mobile machines use electrical energy and are equipped with batteries, for example electric vehicles, cherry pickers, pallet trucks, etc. These machines usually include on-board chargers, in other words, electric battery chargers fitted directly to the mobile machines.
The main function of these on-board chargers is to recharge batteries using electricity available from the electricity supply network.
For reasons of autonomy and efficiency, the traction battery or batteries (which are used to supply power to the traction system, in other words the power train, of the above-mentioned machines) have high voltages (for example 48 V, 60 V or even 400 V or more), whereas the on-board electronics require a lower voltage. The most common nominal voltage is 12 V: it is the voltage required by the items of equipment conventionally used in a motor vehicle environment.
It is therefore necessary to add a DC-DC voltage converter, which lowers the voltage of the traction battery to the value required by the on-board equipment.
It is advantageous to incorporate both this DC-DC converter and the traction battery charging means into the same charging device, to save space, weight, and connectors, achieve greater reliability and facilitate the incorporation of these items of equipment into the vehicle or other motorised machine.
Conventionally, it is known to use the following as a DC-DC converter in a charging device as described above: either a circuit comprising a transformer, which is a heavy and bulky item of equipment; or a step-down (buck) converter, which has no galvanic isolation and which is a safety hazard in the event of failure and short-circuiting of the commutator of the converter (this is because, in this situation, the high input voltage is then applied directly to the output, which can damage the items of equipment operating at low voltage).
There is therefore a need to improve the safety of a charging device for motorised appliance (and in particular for vehicles) including a DC-DC converter, without resorting to equipment that is heavy, bulky and/or expensive.